1. Field of the Invention
This invention relates to a throttle valve control system for internal combustion engines, and more particularly to a throttle valve control system of this kind, which controls the output torque of the engine, by means of a throttle valve-driving mechanism driven by an electric actuator.
2. Prior Art
A throttle valve control system for internal combustion engines is conventionally known, for example, from Japanese Patent Publication (Kokoku) No. 56-37414, which is provided with an electric actuator for driving a throttle valve of the engine and calculates a desired opening of the throttle valve, based on engine rotational speed and required engine torque, to thereby control the actual throttle valve opening to the desired valve opening.
The known throttle valve control system, however, does not contemplate a time lag factor of a change in the pressure within the intake pipe with respect to a change in the throttle valve opening (time lag due to charging and discharging of air into and from a chamber formed in the intake pipe), and as a result, it can undergo degraded response of the engine torque to the operation of the accelerator pedal. Further, according to the known system, the desired opening of the throttle valve is calculated by the use of a map provided with desired throttle valve opening values which have been experimentally determined according to the engine rotational speed and the required engine torque, which can result in an error in the calculated desired valve opening due to aging of the engine or manufacturing tolerances of the same. As a result, the known throttle valve control system cannot accurately control the actual output torque of the engine to the required torque.